Re: wait and spurious wakeups

Patricia Shanahan <>
Tue, 27 Nov 2007 10:37:04 -0800
<fiho57$ek5$> wrote:

Here is my question: what is wrong with calling wait just as wait()?
The developer I am working with claims that wait suffers from the
potential to experience interrupts and spuirous wakeups. Is that
right? He suggested that the following code be used:

synchronized (listOwner) {
    while (special event not received)

Can someone explain this to me please? I have tried talking to the
developer but there is a communication problem (different timezones,
different languages).


The non-looping code would be:

synchronized (listOwner) {
     if(special event not received)

You need to do the test inside the synchronized block to avoid race
conditions where the notifying thread does its notify after the waiting
thread has done its test but before it enters wait.

The difference in cost between doing the "if" and a "while" is so small,
compared to the cost of a wait and inter-thread communication, that you
might just as well use "while", even if you are sure "if" would be
sufficient. It is more robust in the face of future changes, such as
adding use of interrupts.


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